This invention is an implant for placement in the human body and an assembly for so placing that implant. Most desirably, it is an implant for use in the vasculature of the human body and is used to occlude some space in that vasculature as a portion of a treatment regimen. The implant itself is preferably a component of a deployment device using an electrolytically severable joint. The implant component is at least partially covered with a highly resistive or insulative covering. The highly resistive or insulative layer or covering appears to enhance the susceptibility of the electrolytic joint to quick erosion and thus detachment of the implant. Although the implant itself is preferably a vaso-occlusive device, it may instead be a stent, a vena cava filter, or other implant which may be installed in this manner. The implant may be independently coated with insulative or resistive material or may be formed using a material with such as tantalum, which forms such an insulator or resistor in situ.
Implants may be placed in the human body for a wide variety of reasons. For instance, stents are placed in a number of different lumens in the body. They may be placed in arteries to cover vascular lesions or to provide patency to the vessel. Stents are also placed in biliary ducts to prevent them from kinking or collapsing. Grafts may be used with stents to promote growth of endotbelial tissue within those vessels.
Vena cava filters are implanted in the body, typically in the vena cava, to catch thrombus which are sloughed off from other sites within the body and which may be in the blood passing through the chosen site.
Vaso-occlusive devices or implants are used for a wide variety of reasons. They are often used for treatment of intra-vascular aneurysms. This is to say that the treatment involves the placement of a vaso-occlusive device in an aneurysm to cause the formation of a clot and eventually of a collagenous mass containing the vaso-occlusive device. These occlusions seal and fill the aneurysm thereby preventing the weakened wall of the aneurysm from being exposed to the pulsing blood pressure of the open vascular lumen.
Treatment of aneurysms in this fashion is significant improvement over the surgical method typically involved. The surgical or extravascular approach is a common treatment of intra-cranial berry aneurysm; it is straightforward but fairly traumatic. The method involves removing of portion of the cranium and locating the aneurysm. The neck of the aneurysm is closed typically by applying a specially sized clip to the neck of the aneurysm. The surgeon may choose to perform a suture ligation of the neck or wrap the entire aneurysm. Each of these procedures is performed by an very intrusive invasion into the body and is performed from the outside of the aneurysm or target site. General anesthesia, craniotomy, brain retraction, and a placement of clip around the neck of the aneurysm all are traumatic. The surgical procedure is often delayed while waiting for the patient to stabilize medically. For this reason, many patients die from the underlying disease prior to the initiation of the surgical procedure.
Another procedurexe2x80x94the extra-intravascular approachxe2x80x94involves surgically exposing or stereotaxically reaching an aneurysm with a probe. The wall of the aneurysm is perforated from the outside and various techniques are used to occlude the interior of the aneurysm to prevent its rebleeding. The techniques used to occlude the aneurysm include electro-thrombosis, adhesive embolization, hoghair embolization, and ferromagnetic thrombosis. These procedures are discussed in U.S. Pat. No. 5,122,136 to Guglielmi et al., the entirety of which is incorporated by reference.
Guglielmi et al. further describes an endovascular procedure which is at once the most elegant and least invasive. The procedure described in that patent includes a step in which the interior of the aneurysm is entered by the use of guidewire such as those in Engelson, U.S. Pat. No. 4,884,579 and a catheter as in Engelson, U.S. Pat. No. 4,739,768. These patents described devices utilizing guidewires and catheters which allow access to aneurysms from remote parts of the body. Typically, these catheters enter the vasculature through an artery in the groin. The Guglielmi et al system uses catheters and guidewires which have a very flexible distal regions and supporting midsections which allow the combinations to be steerable to the region of the aneurysm. That is to say that the guidewire is first steered for a portion of the route to the aneurysm and the catheter is slid up over that guidewire until it reaches a point near the distal end of the guidewire. By steps, the catheter and guidewire are then placed at the mouth of the aneurysm. The catheter is introduced into the aneurysm and vaso-occlusive or embolism-forming devices may be delivered through the lumen.
Various vaso-occlusive devices are introduced through the noted microcatheters to close the aneurysm site. In some instances, a small balloon may be introduced into the aneurysm where it is inflated, detached, and left to occlude the aneurysm. Balloons are becoming less in favor because of the difficulty in introducing the balloon into the aneurysm sac, the possibility of aneurysm rupture due to over-inflation of the balloon within the aneurysm, and the inherent risk associated with the traction produced when detaching the balloon.
Another desirable embolism-forming device which may be introduced into aneurysm using end of vascular placement procedure is found in U.S. Pat. No. 4,994,069 to Ritchart et al. In that patent are described various devicesxe2x80x94typically platinum/tungsten alloy coils having very small diametersxe2x80x94which may be introduced into the aneurysm through a catheter such as those described in the Engelson patents above. These coils are often made of wire having a diameter of 2-6 mils. The coil diameter is often 10-30 mils. These soft, flexible coils, may be of any length desirable and appropriate for the site to be occluded. After these vaso-occlusive coils are placed in, e.g., a berry aneurysm, they first cause a formation of an embolic mass. This initial mass is shortly thereafter complemented with a collagenous material which significantly lessens the potential for aneurysm rupture.
There are variety of other vaso-occlusive devices, typically coils which may be delivered to the vascular site in a variety of ways, e.g., by mechanically detaching them from the delivery device. A significant number of these devices are described in patents owned by Target Therapeutics, Inc. For instance:
U.S. Pat. No. 5,234,437, to Sepetka shows a method of unscrewing a helically wound coil from a pusher having interlocking surfaces.
U.S. Pat. No. 5,250,071, to Palermo shows an embolic coil assembly using interlocking clasps both on the pusher and on the embolic coil.
U.S. Pat. No. 5,261,916, to Engelson shows a combination pusher/vaso-occlusive coil assembly joined by an interlocking ball and keyway type coupling.
U.S. Pat. No. 5,304,195, to Twyford et al., shows a pusher/vaso-occlusive coil assembly having a fixed proximally extending wire carrying a ball on its proximal end and a pusher having a similar end which two tips are interlocked and disengaged when expelled from the distal tip of the catheter.
U.S. Pat. No. 5,312,415, to Palermo shows a method for discharging numerous coils from a single pusher by using a guidewire which has a section capable of interconnecting with the interior of a helically wound coil.
U.S. Pat. No. 5,350,397, to Palermo et al. shows a pusher having a throat at its distal end and a pusher through its axis. The pusher throat holds onto the end of an embolic coil and releases that coil upon pushing the axially placed pusher wire against member found on the proximal end of the vaso-occlusive coil.
Other mechanically detachable embolism forming devices are known in the art.
Each of the patents listed herein is specifically incorporated by reference.
Guglielmi et al. shows an embolism forming device and procedure for using that device which, instead of a mechanical joint, uses an electrolytically severable joint. Specifically, Guglielmi et al. desirably places a finely wound platinum coil into a vascular cavity such as an aneurysm. The coil is delivered endovascularly using a catheter such as those described above. After placement in the aneurysm, the coil is severed from its insertion core wire by the application of a small electric current to that core wire. The deliverable coils are said to be made of a platinum material. They may be 1-50 cm or longer as is necessary. Proximal of the embolic coil, as noted above, is a core wire which is typically stainless steel. The core wire is used to push the platinum embolic coil into vascular site to be occluded.
Other variations of the Guglielmi et al. technology are found in U.S. Pat. No. 5,354,295.
None of the references described above teach or suggests an implant having a highly resistive or insulative layer on at least a portion of its exterior surface which is flexibly attached to an electrolytically severable delivery joint.
This invention is an implant which is at least partially coated with an insulative material. The implant may be a vaso-occlusive device, stent, vena cava filter, or any other implant which may be delivered via a catheter. Desirably, the device includes a core wire having a distal tip, which distal tip may be introduced into the selected site. The core wire is attached to the distal tip or implant in such a way that it may be electrolytically detached by application of a current to the core wire.
The improvement involves the use of an insulative or highly resistive covering on at least a portion of the implant. The resistive covering is preferably one which is formed in situ from the material making up the implant. This insulative or highly resistive layer appears to focus the current flow through the sacrificial electrolytic joint and thereby improves the rate at which detachment occurs.